CVE-2020-9054Known exploitationPublic exploitNetwork attack vector

Unauthenticated root code execution via username injection

Published Mar 4, 2020 · Updated Oct 21, 2025

OS command injection in Zyxel NAS firmware allows remote attackers to execute arbitrary code as root via crafted HTTP requests. The weblogin.cgi executable passes a username containing shell metacharacters into an OS command without sanitization, and a setuid utility elevates the web-server command to root. No credentials are required; direct web-interface access is sufficient, and a browser can relay a request to a NAS reachable from the client network.

CVSS severity9.8
Critical
EPSS probability99.99%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

OS command injection in Zyxel NAS firmware allows remote attackers to execute arbitrary code as root via crafted HTTP requests. The weblogin.cgi executable passes a username containing shell metacharacters into an OS command without sanitization, and a setuid utility elevates the web-server command to root. No credentials are required; direct web-interface access is sufficient, and a browser can relay a request to a NAS reachable from the client network.

The record

CVE
CVE-2020-9054
Published
Mar 4, 2020
Updated
Oct 21, 2025
Vendor
Zyxel Networks
Product
NAS542 Firmware
Classifications
CWE-78, T1190, T1059.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 4, 2020CVE publishedPublication date reported by the CVE source.
  2. Oct 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=V5.21(ABAG.4)C0 <=V5.21(ABAG.4)C0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Zyxel Networks · NAS542 Firmwareversion=V5.21(ABAG.4)C0 <=V5.21(ABAG.4)C0
Zyxel Networks · NSA210 Firmwareversion=all
Zyxel Networks · NSA325 v2 Firmwareversion=V4.81(AALS.1)C0 <=V4.81(AALS.1)C0
Zyxel Networks · NSA-220 Plus Firmwareversion=all
Zyxel Networks · NSA221 Firmwareversion=all
Zyxel Networks · NAS326 Firmwareversion=V5.21(AAZF.7)C0 <=V5.21(AAZF.7)C0
Zyxel Networks · NSA320S Firmwareversion=V4.75(AANV.2)C0 <=V4.75(AANV.2)C0
Zyxel Networks · NAS540 Firmwareversion=V5.21(AATB.4)C0 <=V5.21(AATB.4)C0
Zyxel Networks · NSA325 Firmwareversion=V4.81(AAAJ.1)C0 <=V4.81(AAAJ.1)C0
Zyxel Networks · NAS520 Firmwareversion=V5.21(AASZ.3)C0 <=V5.21(AASZ.3)C0
Zyxel Networks · NSA320 Firmwareversion=all
Zyxel Networks · NSA310 Firmwareversion=V4.75(AALH.2)C0 <=V4.75(AALH.2)C0

Published CVSS scores

9.5CERT/CCAV:N/AC:L/Au:N/C:C/I:C/A:C/E:F/RL:U/RC:C
10.0CERT/CCAV:N/AC:L/Au:N/C:C/I:C/A:C
9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsShadowserver observations through Sep 16, 2026. Gaps indicate unavailable data.
Sep 10, 2026Sep 16, 2026
View daily counts
Reporting dayUnique IPs
Sep 10, 2026Unavailable
Sep 11, 2026Unavailable
Sep 12, 2026Unavailable
Sep 13, 2026Unavailable
Sep 14, 20261
Sep 15, 2026Unavailable
Sep 16, 20262
Latest reporting daySep 16, 2026
Latest daily unique IPs2
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-78Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
T1190Exploit Public-Facing Application
T1059.004Unix Shell

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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